Multiple sclerosis (MS) is a neurodegenerative autoimmune disease that affects approximately one million people worldwide. There are over 28,000 veterans currently diagnosed with MS. Due to its high prevalence, in 2003, the Veterans Health Administration (VHA) established the MS Centers of Excellence which are committed to serving the health care needs of veterans with MS. There is increased prevalence of symptoms among recent Gulf war and other war veterans which include cognitive dysfunction, depression, chronic fatigue, musculoskeletal complaints, post-traumatic stress disorder and respiratory illness. According to recent testimony by the National Multiple Sclerosis Society (NMSS) to the Subcommittee on Defense, the increasing number of Gulf war veterans exhibiting symptoms described above may actually be suffering from multiple sclerosis. Experimental autoimmune encephalomyelitis (EAE) is an animal model that recapitulates many features of MS in which Th1 and Th17 cells reactive against myelin antigens, cross the blood-brain barrier (BBB), enter the CNS and trigger inflammation, thereby causing demyelination and induction of paralysis. Studies from our laboratory have demonstrated that naove T cells express the standard form of CD44 (CD44s) and upon activation, express certain unique variant isoforms of CD44 (CD44v) through alternative splicing. Specifically, we have shown that CD44 isoforms such as CD44v6/v7 play a critical role in the interaction between activated T cells and endothelial cells (ECs) at sites of inflammation leading to EC injury. Interestingly, we have also noted that CD44 knockout (KO) mice exhibit increased resistance to EAE and decreased neuroinflammation when compared to CD44 wild type (WT) mice. Also, CD44 deficiency on T cells promoted a switch from Th1/Th17 to Th2/Treg differentiation. Preliminary studies also identified unique differences in miRNA expression profiles between CD44 WT and CD44 KO T cells. Based on the above studies, we will test the central hypothesis that naove T cells expressing CD44s, upon activation with myelin antigens presented by the DCs, undergo epigenetic modulation dysregulation in microRNA expression that regulate the transcription of inflammatory cytokine genes leading to promotion of Th1/Th17 differentiation. Furthermore, MOG-reactive T cells express unique CD44v isoforms which promote their interactions with ECs at the BBB via specific ligands, such as hyaluronic acid (HA) and/or osteopontin (OPN). Such an interaction would trigger EC injury and significant damage to the BBB. These events together promote inflammation and demyelination in the CNS. To this end, in the current study, we will identify CD44 variant isoforms expressed on activated MOG- specific T cells and study their role in the pathogenesis of EAE. Next, we will determine how interactions between CD44 with HA or OPN trigger epigenetic regulation by transcription factor gene promoter methylation and/or expression of miRs that lead to a switch in T differentiation from Th1/T17 cells to Th2/Tregs. Pharmacological and genetic intervention will be attempted for reversal of the Th/Treg functions and its effects on EAE. In addition, the interactions between CD44 expressed on antigen-specific T cells and specific ligands on BBB ECs leading to breakdown of BBB and trans-EC migration of T cells into CNS, during EAE, will be tested. Lastly, we will determine if targeting CD44s or CD44v, using strategies that include mimetics, would prevent the development and progression of EAE. Together, our studies should shed new light in understanding the role of CD44 isoforms in the regulation of MS and other inflammatory diseases of the CNS that affect a large proportion of Veterans as well provide novel treatment modalities that would benefit Veterans' health.